The present invention relates to an improvement for an air filter restriction indicating device adapted for use in connection with an internal combustion engine intake air filtration system, and more particularly for an air intake filtration system used with turbo-charged diesel engines in trucks, tractors and other heavy industrial and marine applications. Such an improved device is intended to indicate when the air filter has become so loaded or clogged with contaminants that its cleaning or replacement is required and also to lock itself in various intermediate, indicating positions so as to provide a continuous indication as to how much useful life remains in the air filter before it must be cleaned or replaced. My co-pending application, Ser. No. 273,699 filed June 16, 1981 describes such an air filter restriction indicating device.
While the aforesaid indicating device performs its intended function admirably, experience has shown that there is a possibility that the structure used to reset the indicating device, as when, for example, the air filter has been cleaned or replaced, may be rendered ineffective when the indicating device is used in a wet, cold environment or in a particularly dusty, dirty environment. The indicating device has a housing which encloses most of its components, but a part of the resetting structure is disposed without the housing and is exposed to the environment in which the indicating device is being used. An annulus of filter material surrounds this exposed part of the resetting structure and may become inflexible and stiff because of ice forming therein or thereon or because of dirt caking on or clogging the material. If the annulus is inflexible and stiff, the resetting structure is difficult to actuate and may be rendered ineffective. To minimize this possibility, it is recommended that the indicating device be mounted so that the end of the indicating device including the exposed part of the resetting structure is in a vertically down position, i.e. faced vertically downwardly.
To overcome these problems, the improved indicating device of the present invention includes a novel reset structure that prevents the structure from being rendered ineffective due to dirt and/or ice clogging. The improvement in the reset structure also allows the improved device to be mounted in any position, including in a vertically up position as well as in a vertically down position.